Figure REF (a) shows \(\Delta N_{\mathrm {ch}}(c) = N_{\mathrm {ch,Ru}}(c)-N_{\mathrm {ch,Zr}}(c)\)  and Fig. REF (b) shows \(\Delta c (N_{\mathrm {ch}})=c_{\mathrm {Ru}}(N_{\mathrm {ch}})-c_{\mathrm {Zr}}(N_{\mathrm {ch}})\)  as a function of centrality. Note that \(\Delta N_{\mathrm {ch}}\)  is calculated at matching \(c\) , and \(\Delta c\)  is calculated at matching \(N_{\mathrm {ch}}\) , whose values can be read off directly from Fig. REF  or from analogue plots in the AMPT simulations [1]}. Both \(\Delta N_{\mathrm {ch}}\)  and \(\Delta c\)  can then be presented as a function of either \(c\)  or \(N_{\mathrm {ch}}\) . Since the \(p(N_{\mathrm {ch}})_{\mathrm {Ru}}\)  distribution is broader than \(p(N_{\mathrm {ch}})_{\mathrm {Zr}}\) , events with the same \(N_{\mathrm {ch}}\)  correspond to larger \(c\)  values (or more peripheral collisions) in Ru+Ru than in Zr+Zr. Conversely, events with the same \(c\)  correspond to larger \(N_{\mathrm {ch}}\)  in Ru+Ru than in Zr+Zr. The overall centrality dependence of \(\Delta N_{\mathrm {ch}}\)  and \( \Delta c\)  in Fig. REF  can be qualitatively reproduced by the AMPT model after taking into account the influences of all four WS parameters. We briefly summarize the AMPT results as follows: 1) The diffuseness parameter \(a_0\)  has the largest impact on \(p(N_{\mathrm {ch}})\) , and the smaller \(a_0\)  value of Ru tends to make \(p(N_{\mathrm {ch}})_{\mathrm {Ru}}\)  broader than \(p(N_{\mathrm {ch}})_{\mathrm {Zr}}\) . 2) Half-density radius \(R_0\)  also plays a sizeable role in central collisions, and the larger \(R_0\)  of Ru tends to reduce the range of \(p(N_{\mathrm {ch}})_{\mathrm {Ru}}\)  compared with \(p(N_{\mathrm {ch}})_{\mathrm {Zr}}\) . 3) The effects of nuclear deformation are mostly concentrated in central collisions, with \(\beta _{2\mathrm {Ru}}\)  and \(\beta _{3\mathrm {Zr}}\)  working in the opposite directions.
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